1. Field of the Invention
The present invention relates to a method of reducing the adverse effects of asphaltenes in liquid hydrocarbons and thereby increasing the fluidity of the liquid hydrocarbon. A dispersing agent is added to the liquid hydrocarbon to break up or disassemble agglomerates of asphaltenes and other hydrocarbons containing heteroatoms, e.g. sulfur containing compounds, to reduce the viscosity of the hydrocarbon.
2. Description of Related Art
A need exists to improve the pumpability or fluidity of crude oils and residuums containing asphaltenes so that they can be more easily transported in pipelines, etc. and processed in refineries. Viscous crude oils or "heavy" crude oils are becoming more common in the oil industry and due to their viscous properties they are more costly to handle as compared to the "sweeter" crude oils.
Asphaltenes, due to the polarity of their aromatic rings, agglomerate into very large structures in liquid hydrocarbons. These agglomerates yield viscosities that are much higher than if the asphaltenes were not structured. The usual approach in reducing the viscosity of high asphaltene containing hydrocarbons is to add kerosene or other non-polar distillates. Kerosenes or distillates do not disperse asphaltene agglomerates; they merely dilute the agglomerates to obtain a lower viscosity of lesser extent than if the agglomerates were truly dispersed into individual molecules. Adding kerosene or distillate in sufficient quantities to obtain the desired viscosity can be very costly, especially if the concentrations of the asphaltenes are high.
Addition of kerosene or distillate in some cases can result in more agglomeration and can even cause precipitation of asphaltenes in crude oils. That is, the asphaltenes may, under some circumstances, precipitate to form a sludge which plugs up oil bearing formations and prevents the recovery of additional crude oil from the formations. Also, the sludge can form on valves, on pump impellers, in conduits, etc. and cause adverse mechanical conditions.
It is generally advantageous to keep the asphaltenes in a stable suspension in the hydrocarbon liquid until well into the refining process. This not only increases the ultimate yield but also prevents or reduces the maintenance problems in the process and improves productivity from hydrocarbon formations. Examples of how the prior art has addressed this problem include the following:
U.S. Pat. No. 5,100,531 discloses a method of dispersing asphalt and asphaltenes in crude oil by adding an effective amount of an antifoulant which consists of a mixture of 1) 95-5 weight % of an alkyl substituted phenol-formaldehyde liquid resin having a molecular weight of 1,000 to 20,000 and an alkyl substituent containing 4 to 24 carbon atoms, the alkyl substituent can be a linear or a branched alkyl group, and 2) 5-95 weight percent of a hydrophilic-lipophilic vinylic polymer.
U.S. Pat. No. 5,133,781 discloses a method of stabilizing asphaltenes in hydrocarbons by dissolving the asphaltenes in tetrahydrofuran and then phosphochlorinating the asphaltenes and thereafter reacting the phosphochlorinated-asphaltenes with equimolar amounts of aliphatic or aromatic alcohols.
U.S. Pat. No. 5,494,607 teaches the use of alkyl substituted phenol-formaldehyde resin and various hydrophilic-lipophilic vinyl polymers as asphaltene dispersants. Such combinations enhance the refining of heavy crude oils containing asphaltenes.
U.S. Pat. No. 5,156,975 teaches the use of 40% polyisobutenylsuccinate in as aromatic solvent as asphaltene dispersant antifouling agent. The dispersant can be present in concentrations of about 10 to about 500 ppm.
U.S. Pat. No. 4,752,587 teaches a method of determining the fouling tendency of an asphaltene containing crude oil by the use of thin layer chromatography. The crude oil sample is prepared in the presence of an asphaltene antisolvent; the antisolvent is preferably a combination of a low molecular weight paraffinic hydrocarbon and a hydrocarbon containing polar atoms such as oxygen, nitrogen, chlorine and sulfur.
U.S. Pat. No. 5,132,005 teaches a method of compatibilizing asphaltenes containing bituminous liquids by dissolving the asphaltenes in a solvent, e.g. tetrahydrofuran, and then phosphochlorinating the asphaltene with phosphorous trichloride following by bulk amination of the phosphochlorinated-asphaltene intermediate. This process stabilizes the asphaltene in the bituminous liquid well into the refining process.
It is an object of this invention to improve the dispersion of asphaltene agglomerates in hydrocarbons to lower the viscosity of the hydrocarbon.
It is a further object of the present invention to provide an improved method of lowering the costs for reducing the viscosity of a crude oil or residuum containing asphaltenes by incorporating an asphaltene dispersant to replace a portion of a non-polar diluent, such as kerosene or distillate, that was added to reduce the viscosity.